1. Field of the Invention
The invention relates to a profile for a track, such as a track used on a snowmobile or other tracked vehicle. More particularly, the invention relates to a track that produces less noise and/or vibration when in use than conventional tracks.
2. Description of Related Art
Track drives and their use on vehicles are well known. Conventional track drives typically include one or more continuous tracks, which move in a closed loop. Conventionally, one or more wheels may be used to help keep the track moving in its desired path. Rails or other additional support structures may also be used to help guide the track. Also, conventional track drives typically include a drive wheel or other mechanism to cause the track to move circumferentially, so as to drive the vehicle.
Track drives provide good traction, and can accommodate rough terrain. In addition, because track drives can be made so that they contact the ground (or other surface) with a large area, they are useful for moving across soft or giving surfaces, and for supporting heavy loads.
For these reasons, track drives are commonly used on snowmobiles, which operate primarily on snow and ice, and are often used in difficult terrain.
A snowmobile with a conventional track drive is illustrated in FIG. 1. As may be seen therein, a continuous track 10 is directed in part by one or more wheels 30. The wheels 30 are not powered, but rotate as the track 10 moves.
As may be seen in FIG. 2, a conventional vehicle track consists of a track substrate 11, and may include drive lugs 16 distributed circumferentially along an inner surface 12 of the track 10. Typically, the drive lugs 16 are shaped to provide good engagement between the track 10 and a drive wheel or other drive mechanism (not shown).
In addition, a conventional vehicle track may include terrain lugs 18 distributed circumferentially along an outer surface 14 of the track substrate 11. Typically, the terrain lugs 18 are shaped to engage the terrain on which the vehicle moves, i.e. snow and ice for the snowmobile illustrated in FIG. 1.
A magnified view of a section of a conventional track 10 is shown in FIG. 2.
A conventional track typically is constructed of some flexible material, so that it bends as it passes around the drive mechanism, wheels, and/or other guide structures. Exemplary arrangements of wheels 30 that make up a portion of a conventional suspension system for a tracked vehicle may be seen in FIGS. 3-5.
It is noted that the individual wheels in a given track system may have different functions, different sizes, etc. For example, certain of the wheels 30 shown in FIGS. 3-5 are used to change the direction of a track, while other wheels 30 shown therein are used to support the vehicle's weight and transfer it to the track, to keep the track from contacting other components, or to perform other functions. Wheels may have names specific to their function or location, i.e. “idler wheel”, “roller wheel”, etc. However, for purposes of this application, the precise nature and function of the wheels is of concern primarily insofar as the wheels interact with a track to produce noise and vibration. For this reason, the wheels are referred to collectively herein, although they may not be identical in form or function.
As is visible from FIG. 2, the presence of the drive lugs 16 and the terrain lugs 18 significantly increases the thickness of the track 10 at some points along its circumference. Even if the drive lugs 16 and terrain lugs 18 also are made of flexible material, the track 10 often is much less flexible in the vicinity of the drive lugs 16 and the terrain lugs 18 at least in part because of the increased thickness. In addition, as shown in FIG. 2, conventional tracks 10 may be deliberately made stiffer in the vicinity of the drive lugs 16 and terrain lugs 18, for example by including bars 17 of relatively rigid material therein.
One result of this may be seen in FIG. 6. FIG. 6 shows a schematic view of a portion of a conventional track 10 where it passes around a wheel 30, changing direction as it does so. Because the track 10 is thicker near the drive lugs 16 and terrain lugs 18, it is relatively rigid there. As a result, the track 10 does not bend readily in the areas near the drive lugs 16 and terrain lugs 18, and those areas of the track 10 remain relatively flat. Most or all of the bending of the track 10 occurs in areas in between adjacent drive lugs 16 and terrain lugs 18.
As may be seen from FIG. 6, with such an arrangement, a conventional track 10 does not fit closely to a conventional wheel 30 while changing direction around the wheel 30. As illustrated, the track 10 actually makes contact with the wheel 30 only in the immediate vicinity of the drive lugs 16 and terrain lugs 18.
It is believed that such an arrangement contributes to the generation of noise and vibration as the track 10 moves around the wheel 30. For example, as the track 10 moves around the wheel 30, the track 10 makes contact with the wheel 30 only at intermittent points, rather than smoothly engaging the wheel 30. This process is essentially a series of impacts between the track 10 and the wheel 30, which may generate considerable noise and/or vibration.
In addition, in the areas between the drive lugs 16 and terrain lugs 18, the track 10 is unsupported. The track 10 in those areas is free to move back and forth with any existing vibrations or impacts, potentially causing it to strike the wheel 30. This also may contribute to the noise and vibration produced by the track drive.
Interaction between a conventional track 10 and wheels 30 may also contribute to noise and vibration in other ways, even if the track is not changing direction as shown in FIG. 6.
For example, in FIG. 7 two wheels 30 are shown in schematic form in an arrangement wherein they support at least part of the weight of a vehicle. The wheel 30 that is shown to be aligned with a drive lug 16 and terrain lug 18 does not appreciably deform the track 10. However, the wheel 30 that is shown to be between adjacent drive lugs 16 and terrain lugs 18 does deform the track 10; the weight of the vehicle presses the wheel downward.
The phenomenon illustrated in FIG. 7, which is sometimes referred to as “bridging”, results in the wheels 30 moving up and down as the track 10 moves. This motion is in some ways similar to what would occur if a wheel is made to move over a series of fixed obstacles in its path. The noise and/or vibration may resulting from such motion may be considerable.
It is noted that in actuality, the deformation of the track 10 between adjacent drive lugs 16 and terrain lugs 18 may be sinusoidal, or otherwise curved. However, for clarity it is pictured as straight-line deformity in FIG. 7.
Regardless of the precise source(s), it may be desirable to reduce the noise and/or vibration generated in conventional track drives. For example, track vibration may be unpleasant for the vehicle operator, and track noise likewise may be disadvantageous to the vehicle operator and/or persons nearby. In addition, mechanical vibrations may contribute to wear on the track drive and/or other vehicle components.